More than one reissue application has been filed for the reissue of U.S. Pat. No. 5,522,283. The reissue applications are application Ser. No. 09/453,954 (the present application) and Ser. No. 09/090,763(now U.S. Pat. No. Re. 36,409) of which Ser. No. 09/453,954 is a continuation of reissue application 09/090,763 filed Jun. 4, 1998.
This invention relates to a circular saw blade straightening and tensioning machine for eliminating unevenness in and tensioning circular saw blades and, more particularly, to such a machine having straightening rollers disposed on both sides of the saw blade.
When a circular saw operates at the high rate of rotation necessary to cut wood, the outer edges of the blade have a tendency to deviate from the cutting line, either to one side or the other, or to both sides, producing a wavy cut. There is also a tendency for the saw edge to start its cut to one side or the other of the intended line, whereupon the blade tends to lead the cut in that direction. Paradoxically, when the blade is stopped, it is found to be straight and true.
The uneven cutting above described is a result of invisible defects in the saw blade, which defects include both minute surface deformities and improper distribution of residual tension stresses in the blade. The centrifugal force which results from high-blade rotational speeds induces substantial tension stress in the blade. This tension is superimposed on any residual stresses in the blade, such that the resulting non-uniformity of tension produces uneven strain. Any irregularities in the blade surface also interfere with true running, as the tension changes when the blade approaches its cutting speed. Thus, a blade may be deflected from a true course by either of these types of defects.
Areas on the surface of a blade wherein residual tension stresses vary significantly from the normal tension level in that portion of the blade are commonly referred to as xe2x80x9ctightxe2x80x9d or xe2x80x9cloosexe2x80x9d spots. Surface deformities as above noted include convex and concave deviations from a flat plane, including bulges, ridges, kinks, etc. Consequently, a critical part of the maintenance of circular saws is removing these dents or bends, i.e., leveling, as well as tuning the saw plate to operate at typical rotational speeds by stretching the plate in specifically determined locations to cause tension at the periphery of the saw plate, i.e., tensioning.
Leveling and tensioning operations have typically been done manually using various hammers, anvils and gauges. Indeed, several equipment manufacturers build xe2x80x9cstretcher rollsxe2x80x9d which assist in such manual tensioning and leveling of saw blades.
Manual tensioning and leveling is a highly skilled craft requiring intuitive analyses of problems and the development of unique solutions. Workers who do this are known as sawsmiths. They are among the highest paid of all shop trades. Because of the great skill required, the number of sawsmiths practicing this trade has remained greatly limited and the craft has often been practiced in secret. Besides the hammers, anvils, straight edges and other tools, the sawsmith must utilize his senses. These must be trained by long experience such that he can inspect a saw blade for imperfections, mark the blade as to type and location of imperfections, and then employ the proper hammering patterns and tools to remove the imperfections from the saw. Proper hammering over both surfaces produces a more uniform tension distribution, as well as removing surface flaws, thereby to enable the saw to run straight and true at cutting speeds.
In order for a sawsmith properly to hammer a saw blade, generally he first bends it around an axis parallel to one of its diameters so that its surface takes the form of a curved cylindrical segment. This is called xe2x80x9cdishingxe2x80x9d the blade. The sawsmith then applies a straight edge to the blade surfaces at right angles to their curvature. The blade reveals to his practiced eye the nature and location of any defects. The sawsmith then marks each defect such that he may thereafter select those tools and techniques best suited for its correction. Typically, the sawsmith places the saw on an anvil and commences hammering the marked areas, guided only by his marks. Of course, he must be extremely careful to hammer in the proper manner and in the correct location. While performing this rectifying operation, the sawsmith may also hammer generally over the entire surface of the saw blade, thereby to obtain an overall distribution of tension appropriate to the particular blade involved.
When he applies his straight edge as above described, the sawsmith actually is locating bulges and depressions representing either physical distortions or xe2x80x9ctightxe2x80x9d or xe2x80x9cloosexe2x80x9d spots on the surface of the blade. Tight spots on the blade surface tend to bulge inwardly from the concave surface when the saw is bent or dished. Similarly, loose spots tend to bulge outwardly. When the blade is laid flat, such areas generally cannot be detected. Kinks, ridges and other physical distortions in the blade can also be detected by the way they stand up under a straight edge. Additionally, the manner in which the saw blade actually curves when it is bent or dished is, to the skilled hand and eye of the sawsmith, a measure of the overall tension distribution in the saw. As can be readily understood, proper leveling and tensioning of a saw blade is a highly skilled art, the cost of which is quite significant.
In view of the cost inherent in proper manual hammering of a saw, it was natural that the trade would attempt to create a machine which could accomplish such hammering at lesser cost. U.S. Pat. No. 510,210 was an early attempt at achieving a device which could be used to straighten circular saws. The apparatus therein disclosed provided rollers or blocks on both sides of the saw blade which were so disposed in relation to one another that the blade could be deformed in a direction opposite to that of the distortion.
U.S. Pat. No. 1,053,746 disclosed a similar machine utilizing rollers which moved toward and away from each other. The rollers were arranged to take a circular course over the surface of the saw, or, alternatively, a spiral course, in which case they could automatically feed the saw. Transverse movements of the saw-supporting structure were themselves monitored by a hand lever. U.S. Pat. No. 1,096,756 disclosed an improvement to the ""746 patent and, in particular, to the saw-supporting and saw-controlling structure thereof.
U.S. Pat. No. 1,290,491 disclosed another circular saw stretching and tensioning machine wherein a pair of straightening rollers were each coaxially mounted on shafts positioned parallel to the sides of the saw blade.
U.S. Pat. No. 3,964,348 disclosed a circular saw blade hammering machine utilizing a proximity detector and wherein the blade was dished to locate tight and loose portions. A hammer was utilized to strike the blade wherever a high spot was detected. The action of the hammer was meant to replicate that of the sawsmith during his manual operations.
U.S. Pat. No. 4,852,430 disclosed a band saw blade straightening machine with sensor means for scanning the surface of the blade and generating a signal responsive to unevenness therein. A straightening station with two pairs of straightening rollers was provided. The straightening rollers comprised two pairs of rollers. One pair had a roller disposed above the band saw with a convex roller surface for smoothing upwardly directed unevenness, and a roller with a concave rolling surface disposed opposite underneath the band saw. The other pair for smoothing downwardly directed unevenness had a roller disposed above the band saw with a concave rolling surface and a roller with a convex rolling surface disposed underneath. The machine, however, was unsuitable for circular saw blades because it is not possible to define straight pathways with straightening rollers and a sensor behind each on a circular saw blade.
U.S. Pat. No. 4,875,393 disclosed an apparatus having a pair of top rolls and a pair of bottom rolls with one of the top rolls and one of the bottom rolls in each pair being of larger diameter than the other of the pair in both top and bottom positions. By providing a pair of rolls at the top and a second pair at the bottom with one of the two rolls in each pair being larger in diameter than the other, better leverage was allegedly possible to distort a saw blade either up or down.
U.S. Pat. No. 5,269,205 disclosed still another saw blade straightening machine wherein the blade was scanned with an electronic indicator mounted with a fixed reference from a beam. This scanner or sensor is unable to supply proper usable information to the computer which governs the action of the pressing rollers. Specifically, referencing a sensor from a fixed beam fails to recognize that a typical defect in a saw blade is often actually the result of three bends.
For example, a bulge in an upper surface of a saw blade is often the result of two concave deformations, which cause a convex deformation therebetween. The sensor disclosed in the ""205 patent is unable to detect the fact that, in many such cases, only the concave areas are the actual defective areas, the apparent bulge being in fact a convex area, which is the natural result of the concave areas on either side. A sensor referenced from a fixed beam can only find and attempt to correct the convex area between the two concave areas.
Furthermore, the sensor disclosed in the ""205 patent must be calibrated for each plate thickness. Also, the sensor disclosed has a very tiny contact point which is vulnerable to wear-related errors. Also, a properly tensioned saw plate may sag at its periphery when positioned horizontally and supported only at its center eye. The ""205 patent sensor detects this condition as a very long dent down and, consequently, relays erroneous information to the computer.
Additionally, the ""205 patent machine requires two complete sets of rollers, one set and all its supporting assemblies to push a convex deformation downwardly, and an additional set of rollers with an additional set of supporting assemblies to push a concave deformation upwardly.
Accordingly, it is an object of the present invention to provide a circular saw blade straightening and tensioning machine requiring only one set of rollers and only one supporting assembly therefor.
It is a further object of the invention to provide a circular saw blade straightening and tensioning machine with a single set of unique straightening rollers that can push a dent up, push it down, or stretch the plate, depending upon the particular need.
It is a further object of the invention to provide a circular saw blade straightening and tensioning machine with a sensor that can identify the actual bend area, rather than merely locating a deflected area in the plate.
It is a further object of the present invention to provide a circular saw blade straightening and tensioning machine having a floating sensor instead of a sensor referencing from a fixed beam, the floating sensor being able to detect deformations including concave regions which cause a convex area therebetween, thereby to be able to work each area individually as required.
It is a still further object of the present invention to provide a circular saw blade straightening and tensioning machine wherein the sensor does not have to be calibrated for different plate thicknesses.
It is a still further object of the present invention to provide a circular saw blade straightening and tensioning machine as above described wherein the sensor has large carbide wear surfaces having a very long life cycle.
It is a still further object of the present invention to provide a circular saw blade straightening and tensioning machine wherein the sensor is able to distinguish between a saw blade having deformations therein that require correction and a properly tensioned saw blade which sags at its periphery merely because of the way it is supported.
My circular saw blade straightening and tensioning machine comprises a mounting adapted rotatably to support a circular saw blade. A single set of rollers is provided, which set includes rollers adapted to be disposed on both sides of the saw blade. The axis of the set in its operating position is concurrent with a radius of the saw blade. The set is movable along the radius from the center to the periphery thereof. The roller set includes an upper shaft and a lower shaft. Each of the upper and lower shafts is disposed parallel to the upper and lower surfaces of the saw blade, respectively.
A hub is mounted on one end of each of the upper and lower shafts of the roller set. Each of the hubs includes a center portion horizontally offset or eccentric with respect to the centerline of its respective shaft, and a pair of side portions disposed on opposite sides of the center portion. Each of the side portions is also horizontally offset or eccentric with respect to the centerline of its respective shaft, but in a direction opposite to that of the center portion. A roller is rotatably mounted on each of the center and side portions of each of the hubs. Each of the rollers has the same outer diameter.
An actuator is provided to rotate each of the upper and lower shafts selectively ninety degrees in the clockwise and counterclockwise directions. The actuator provides the necessary deforming force.
Rotation by the actuator of the upper shaft in one of the clockwise and counterclockwise directions forces the rollers on the side portions of the hub on the upper shaft downwardly against the upper surface of the saw blade. Simultaneous rotation of the lower shaft by the actuator in the same direction forces the roller on the center portion of the hub on the lower shaft upwardly against the lower surface of the saw blade. The downward movement of the rollers on the side portions of the hub on the upper shaft combines with the upward movement of the roller on the center portion of the hub on the lower shaft to force upwardly a downwardly extending unevenness in the saw blade.
Similarly, rotation of the upper shaft by the actuator in the other of the clockwise and counterclockwise directions forces the roller on the center portion of the hub on the upper shaft downwardly against the upper surface of the saw blade. Simultaneous rotation of the lower shaft by the actuator in the same direction forces the rollers on the side portions of the hub on the lower shaft upwardly against the lower surface of the saw blade. The downward movement of the roller on the center portion of the hub on the upper shaft combines with the upward movement of the rollers on the side portions of the hub on the lower shaft to force downwardly an upwardly extending unevenness in the saw blade.
Furthermore, rotation of the lower shaft by the actuator in one of the clockwise and counterclockwise directions and simultaneous rotation of the upper shaft by the actuator in the other of the clockwise and counterclockwise directions forces the roller on the center portion of the hub on the upper shaft downwardly against the upper surface of the saw blade and the roller on the center portion of the hub on the lower shaft upwardly against the lower surface of the saw blade. The resulting downward movement of the roller on the center portion of the hub on the upper shaft combines with the upward movement on the roller on the center portion of the hub on the lower shaft to exert a compression force on the saw blade at the point of contact, thereby to tension the blade.
Finally, a sensor is provided to scan one surface of the saw blade in advance of the rollers. The sensor generates a signal to the set of rollers in the event of unevenness in the saw blade in either the upward or downward directions.
The sensor is adapted to move along a radius of the saw blade and to scan the upper surface thereof. The sensor includes a frame, preferably a rectangular frame, having at least three, and preferably four, fixed foot supports. These fixed foot supports have flat contact surfaces for sliding along the upper surface of the saw blade. The contact surfaces of the supports define a flat plane.
A movable foot is pivotally mounted from the frame centrally of the fixed supports. The movable or pivotable foot, which is also flat, contacts the upper surface of the saw blade intermediate the fixed supports at a point along the radius of the blade.
A gauge is connected to the movable or pivotable foot. The gauge can measure upward and downward deviation of the upper surface of the saw blade from the plane defined by the fixed supports along the radius of the blade. The gauge generates a signal proportional to such deviation. The rollers can then exert upward and downward pressure on the saw blade at such point as required, responsive to the signal.
The set of rollers and the sensor are displaceable by the same distance towards the center or towards the periphery of the saw blade, i.e., they are tied together to act at the same radial distance from the center of the saw. The sensor is positioned on a radius preferably ninety degrees in advance of the radius with which the axis of the set of rollers is concurrent.
The set of rollers is preferably mounted on a first carriage. The carriage is adapted to mesh with a ball screw or threaded spindle mounted on a base plate. The carriage is driven along the spindle by a motor adapted to rotate the same. Rotation of the spindle by the motor drives the carriage to move the set of rollers along a radius of the blade.
The sensor is preferably mounted on a second carriage which itself is mounted on a track mounted on the baseplate. The track preferably makes an angle of ninety degrees with the axis of the threaded spindle. The second carriage is mounted on the track and is adapted to be driven therealong by chain means which connect the first and second carriages. Rotation of the spindle driving the first carriage in a direction toward or away from the center of the saw blade causes the chain means to pull the second carriage the same distance in the same direction.
The chain means preferably comprises a pair of sprockets coaxially mounted on the baseplate and adapted to rotate with respect thereto. A first chain is attached at its ends to the first carriage carrying the rollers, and such first chain is entrained around one of the sprockets of the pair in order to rotate the same. A second chain is attached at its ends to the second carriage on which the sensor is mounted. The second chain is entrained around the second of the sprockets of the pair and is adapted to be rotated thereby. In this manner, movement of the first carriage rotates the first chain and the first sprocket, which causes rotation of the second sprocket. This causes movement of the sensor on the second carriage a distance equal to the movement of the set of rollers on the first carriage.
The first carriage on which is mounted the set of rollers includes a first arm pivotally mounted thereto. The lower shaft of the set of rollers is supported by such first arm. A second arm is pivotally mounted to the first arm. The upper shaft of the set of rollers is supported by such second arm. In this manner, the upper and lower shafts of the set can be separated to permit the circular saw blade to be placed on its rotatable mounting and between the rollers.
A first air cylinder is mounted on the first arm carrying the lower shaft of the set of rollers. A piston is disposed within the first cylinder and a piston rod is attached to the piston. The rod extends downwardly to bottom on the first carriage on which is mounted the set of rollers. In this manner, retraction of the first piston rod permits the first arm to rotate downwardly to lower the lower shaft and the rollers mounted thereon. Similarly, extension of the piston rod rotates the first arm upwardly to raise the lower shaft and place the rollers mounted thereon adjacent the lower surface of the saw blade and in a working position.
A generally vertical extension is attached to the second arm carrying the upper shaft of the set of rollers. Such extension extends above the second arm. A second air cylinder is mounted on the extension and depends therefrom. A second piston is disposed within the second air cylinder and a second piston rod is attached at its upper end to the second piston. The second piston rod is attached at its lower end to the second arm. In this manner, retraction of the second piston rod rotates the second arm upwardly to raise the upper shaft and the rollers mounted thereon. Similarly, extension of the second piston rod rotates the second arm downwardly to lower the upper shaft and place the rollers mounted thereon adjacent the upper surface of the saw blade and in a working position.
Means are provided to introduce a selected amount of air pressure into the upper end of the second air cylinder upon extension of the second piston rod to limit the amount of force applicable by the actuator through the rollers against the upper and lower surfaces of the saw blade to the amount of air pressure so selected. In this manner, correction of deformations in the surface of the blade can be achieved in several stages.